Sputtering is a well-known technique for depositing uniform thin films on a particular substrate. Sputtering is performed in an evacuated chamber using an inert gas, typically argon, with one or more substrates being transported past the target. An exemplary sputtering technique is magnetron sputtering which utilizes magnetrons. Examples of such magnetron sputtering techniques, such as planar magnetron sputtering and rotary magnetron sputtering are discussed in U.S. Pat. No. 7,544,884, issued on Jun. 9, 2009, and which is hereby incorporated by reference in its entirety.
Typically, evacuation of the sputtering chamber is a two-stage process in order to avoid contaminant-circulating turbulence in the chamber. First, a throttled roughing stage slowly pumps down the chamber to a first pressure, such as about 50 mtorr. Then, high vacuum pumping occurs using turbo or diffusion pumps to evacuate the chamber to the highly evacuated base pressure (about 10E-6 Torr) necessary to perform sputtering. Sputtering gas is subsequently provided in the evacuated chamber, backfilling to a pressure of about 2-10 mtorr.
The sputtering process is useful for depositing coatings from a plurality of target materials onto a various substrate materials including glass, stainless steel, plastics, and ceramic materials. However, the relatively low sputtering rate achieved by the process solely relying on electrostatic forces (diode sputtering) may be impracticable for certain commercial applications where high volume processing is desired. Consequently, various magnet arrangements have been used to enhance the sputtering rate by trapping electrons close to the target surface, ionizing more argon, increasing the probability of impacting and dislodging target atoms and therefore the sputtering rate. In particular, an increased sputtering rate is achieved by manipulation of a magnetic field geometry in the region adjacent to the target surface. Sputter deposition performed in this manner is generally referred to as magnetron sputtering.
The role of the magnetic field is to trap moving electrons near the target. The field generates a force on the electrons, inducing the electrons to take a spiral path about the magnetic field lines. Such a spiral path is longer than a path along the field lines, thereby increasing the chance of the electron ionizing a plasma gas atom, typically argon. In addition, field lines also reduce electron repulsion away from a negatively biased target. As a result, a greater ion flux is created in the plasma region adjacent to the target with a correspondingly enhanced erosion of target atoms from an area which conforms to a shape approximating the inverse shape of the field lines. Thus, if the field above the target is configured in arcuate lines, the erosion region adjacent to the field lines conforms to a shallow track, leaving much of the target unavailable for sputtering.
To overcome the low utilization of sputtering targets the application of electromagnetic coils in combination with permanent magnets has been used to sweep the magnetic field across the surface of the target using an adjustable power supply connected to the electromagnetic coils, which thereby increases the region of erosion on the target surface and the overall utilization of target material.
However, in magnetron sputtering systems that rely on power supplies with high frequency pulsed power signals the inventors have discovered an unwanted coupling between the magnetron power supplies and the electromagnetic coil power supplies, resulting in greatly reduce reliability and an increased rate of failure in the switching systems that control the polarity of current delivered to the electromagnetic coils.